Blasting initiator



July 21, 1964 R. P. GUNDLACH ETAL 3,141,410

BLASTING INITIATOR Filed Feb. 8, 1962 FIGA Br f'/ .4/

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States York Filed Feb. S, 1962, Ser. No. 174,345 7 Claims. (Cl. 102-24)The present invention pertains to initiators, and more specifically, toinitiators which are relatively insensitivel to impact, friction andburning and yet are very effective in achieving high order detonation.

This is a continuation-in-part of application, Serial No. 20,376, filedApr. 6, 1960, now abandoned.

An initiator is a relatively small compact explosive composition that isused to detonate a larger or main body explosive such as the ammoniumnitrate-oil mixture. The initiator sets up the last step in the chainreaction of setting off a large body of explosive. The detonationprocess proceeds through the following stages: detonating cord, booster,initiator and main body explosives, each stage rendering a largerexplosive force than the preceding stage and each subsequent stagerequiring the larger explosive force to detonate it. Initiatorsheretofore known have had the disadvantages of requiring considerabletedium in the application of a booster or the attachment of theprimersuch as detonating cordat the point of use.

Therefore, it is an object of the present invention to provide aninitiator having, and a mode of making it with, a built-in booster, butwhich is relatively insensitive, except in purposeful detonation, andwhich is safe to handle.

Further objects will appear from the detailed description taken inconnection with the drawings in which:

FIGURE l is a top view of the initiator; and

FIGURE 2 is a cross-sectional view of the initiator.

According to the present invention, the initiator consists of a block ofa suitable explosive composition molded into a container and having castin situ therein a short cylinder of large size detonating cord to serveas a booster element. During the casting of the composition, there ismaintained therein two passageways passing vertically through thecomposition. The booster element is cast in situ within the explosivecomposition in such a manner that its ends are exposed at at least oneof the vertical passageways. When the initiator is to be detonated, asmaller size detonating cord is passed through one or both of thevertical passageways and secured in position. When the detonating cordis detonated and the detonation wave reaches the booster element, thebooster element will detonate thereby detonating the initiator.

Referring now to the drawings, a block of explosive 1 is cast in situwithin a suitable container 2 formed of paper, or other suitablematerial. The container 2 has a base 3, in which there is a pair ofspaced apertures 7. The explosive composition may be, and usually is,selected so as to have detonation characteristics which will detonatethe main body of a blasting agent. Where the blasting agent is a commonone such as the well-known ammonium nitrate-oil mixture, the explosiveelement 1 is preferably composed according to any one of the followingexamples:

(A) An explosive composition containing 50% TNT (trinitrotoluene) and50% PETN (pentaerythritol tetranitrate).

(B) Composition B-containing 60% RDX (cyclotrimethylenetrinitramine),38% TNT (trinitrotoluene) and 2% eeswax.

. PETN) therein.

(C) An explosive composition containing 98% RDX and 2% beeswax.

The shape of the explosive block 1 depends upon the shape of thecontainer, but is preferably a cylinder on the order of three inches indiameter and two inches in axial dimension. The molding may beaccomplished either by melting and pouring the explosive, or by pressingplastic granules into cohesion. Ineither event, during the castingoperation, a pair of steel pins (not shown) project upwardly from asuitable base (not shown) through apertures 7 to a position above thelevel of the top of container 2. Hence, the pins protrude through whatwill subsequently become the block of explosive, and when the pins arewithdrawn, they will leave open passageways 4 through the block 1.Preferably prior to the beginning of the molding operation, a booster 5is wedged endwise between the 1aforesaid pins. The booster 5 preferablyconsists of a short cylinder cut from a length of large size detonatingcord, as, for example, Primacord winch is 0.4 inch in diameter, andhaving 400 grains of pentaerythritol tetranitrate (hereinafter referredto as PETN) per foot. If desired, however, the container 2 may bepartially filled with the explosive composition before the booster 5 iswedged between the pins. In either event, the container Z is filled, orsubstantially filled, with explosive composition, so as to completelyenvelop booster 5, except at the ends which are adjacent the aforesaidpins, and which, when the pins are removed, will be exposed on theinterior of passageways 4. Booster element 5 is thus cast in situ inblock l. When the explosive composition has set solid, the container 2and its contents are removed from the pins and lid 6 applied thereto.

The passageways 4 are of such size as to accommodate a strand ofdetonating cord of the size and character used for setting off anexplosion from a remote point. Typical of such detonating cord is aplastic or braided tube, 0.2 inch in diameter, containing 50 grains perfoot of PETN, and having a detonation rate of 20,000 feet per second.The detonating cord, from which the short cylinder forming boosterelement 5 is cut, is of similar construction, except that it is largerin diameter, and contains, for example, 400 grains of PETN per foot.

The booster element 5, however, may have a variety of shapes and sizessince these are not vultimately important in the overall operatingability of the initiator. The important features, rather, reside in thepositioning of the booster element within the initiator and the contentor amount of explosive material (such as RDX or We have found that about15 grains of the explosive material is necessarily present in thebooster element to obtain detonation. However, numerous tests have beenrun, showing that a booster element containing about 50 grains ofexplosive material renders the initiator 100% reliable, while stillmaintaining a high safety factor; therefore, the preferred amount ofexplosive material present in the booster element should be about 50grains. It is believed that any more than about 60 grains of theexplosive material would be uneconomical, however, the present inventionis inclusive of such amounts.

Initiators having booster elements molded in situ containing about 50grains of explosive material, have successfully survived numerous safetytests which are well known to those skilled in the art, such as thependulum swing, the block drop and burning tests, with no detonationsresulting therefrom.

The following specific examples are representative of the initiators ofthe present invention, but the invention is not deemed to be limitedthereby.

. 3 Example I A 11/2 inch piece of 400 grain Primacord (400 grains ofPETN per foot) .4 inch in diameter was molded in situ in a block ofComposition B. The resulting initiator had a diameter of about 3 inches.Initiators of this type have a 100% reliability whenl purposelydetonated, while not being detonated by any of the safety testprocedures above stated.

Example II A cardboard tube .4 x 1.5 containing 3.3 grams (about 51grains) of RDX was molded in situ in a block of Cornposition E. Theresulting initiator had a diameter of about 3 inches. Initiators of thistype have a 100% reliability when purposely detonated, and possess ahigh safety factor in that they were not detonated by any of the safetytest procedures above stated.

Example III A one inch piece of 400 grain Primacord (about 34 grains ofPETN) was molded in situ on a block of Cornposition B. The resultinginitiator had a diameter of about 2 inches. lnitiators of this type havean 80 plus percent reliability with a high safety factor as abovedescribed.

In order to prevent the loss of PETN at the cut ends of the boosterelement 5, suitable caps 8 of paper, plastic, or any other materialwhich does not interfere with the transmission of the explosive wavefrom the small detonating cord to the booster, may be applied.

The steel pins which form openings 4 in the cast block are preferablycoated with a suitable mold release composition, in order to facilitatevtheir removal after the explosive composition has solidified and set.

In the use of the device for detonating blasting charges, the lid 6 isfirst removed, and a strand of detonating cord, approximately 0.2 inchesin diameter as aforesaid, is threaded through one or both openings 4,and suitably affixed. The last-mentioned detonating cord will be ofsuiicient length to extend to the remote point at which it is to bedetonated, and the container 2 will be planted in a position such as todetonate the blasting charge.

From the foregoing description, it is evident that the invention is notlimited to the details of construction shown in the specic embodiments,and so it is further apparent that operable substitutions for theexplosive composition may be readily made without departing from thepresent invention. It is therefore understood that the invention is notlimited to the specic details shown and described.

Many changes in and modifications of the construction described may bemade without departing from the spirit of our invention or sacrificingits advantages.

Having thus described the invention, what is claimed and desired to besecured by Letters Patent is:

1. An initiator comprising a molded block of explosive compositionhaving cast in situ therein an encased cylinder of explosive material inan amount within the range of about l to about 60 grains, said cylinderhaving its ends each adjacent to a Vertical passageway passing throughthe molded block, wherein said cylinder is located entirely between saidpassageways, and said passageways having a size such as to accommodate astandard strand of detonating cord.

2. An initiator comprising a molded block of Composition B having castin situ therein an encased cylinder of PETN in an amount within therange of about l5 to about 60 grains, said cylinder having its ends eachadjacent to a vertical passageway passing through the molded block,wherein said cylinder is located entirely between said passageways, andsaid passageways having a size such as to accommodate a standard strandof detonating Cord.

3. An initiator comprising a molded block of explosive compositionhaving cast in situ therein an encased cylinlinder of RDX in an amountwithin the range of about 15 to about 60 grains, said cylinder havingits ends each adjacent to a vertical passageway passing through themolded block, wherein said cylinder is located entirely between saidpassageways, and said passageways having a size such as to accommodate astandard strand of detonating cord.

4. An initiator comprising a molded block of Composition B having castin situ therein an encased cylinder of RDX inV anY amount with the rangeof about 15 to about 60 grains, said cylinder having its ends eachadjacent to a vertical passageway passing through the molded block,wherein said cylinder is located entirely between said passageways, andsaid passageways having a size such as to accommodate a standard strandof detonating cord.

5. An initiator comprising a molded block of explosive compositionhaving cast in situ therein an encased cylinder of PETN in an amountwithin the range of about 15 to about 60 grains, said cylinder havingsits ends each adjacent to a vertical passageway passing through themolded block, wherein said cylinder is located entirely between saidpassageways, and said passageways having a size such as to accommodate astandard strand of detonating cord.

6. An 'initiator comprising a molded block of Composition B having castin situ therein an encased cylinder of PETN in an amount of about 50grains, said cylinder having its ends each adjacent to a verticalpassageway passing through the molded block, wherein said cylinder islocated entirely between said passageways, and said passageways having asize such as to accommodate a standard strand of detonating cord.

7. An initiator comprising a molded block of Composition B having castin situ therein an encased cylinder of RDX in an amount of about 50grains, said cylinder having its ends each adjacent to a verticalpassageway passing through the molded block, wherein said cylinder islocated entirely between said passageways, and said passageways having asize such as to accommodate a standard strand of detonating cord.

References Cited in the iile of this patent UNITED STATES PATENTS2,709,407 Lowe May 31, 1955 2,775,200 Guenter Dec. 25, 1956 2,913,982Hayes Nov. 24, 1959 2,944,485 Ely et al July 12, 1960 3,037,452 Cook etal. June 5, 1962 3,037,453 Cook et al. June 5, 1962` Le.. .e

1. AN INITIATOR COMPRISING A MOLDED BLOCK OF EXPLOSIVE COMPOSITIONHAVING CAST IN SITU THEREIN AN ENCASED CYLINDER OF EXPLOSIVE MATERIAL INAN AMOUNT WITHIN THE RANGE OF ABOUT 15 TO ABOUT 60 GRAINS, SAID CYLINDERHAVING ITS ENDS EACH ADJACENT TO A VERTICAL PASSAGEWAY PASSING THROUGHTHE MOLDED BLOCK, WHEREIN SAID CYLINDER IS LO-